What to expect during demolition

What to expect during viaduct demolition

Removing a concrete highway in a dense, urban environment will be unavoidably disruptive. Kiewit, the contractor conducting the work, has carefully designed their work to reduce disruption where possible to people living, working, and travelling nearby.

How to stay informed

The primary goal of both WSDOT and Kiewit is to remove the viaduct safely and quickly, while reducing construction's effects on people nearby. Read below for more information on what you can expect if you live, work or travel near the job site.

Overall schedule

Removing the whole viaduct will take about six months, with the contractor working on the viaduct in multiple places at once to speed up the overall pace of work. The schedule is below, but visit our demolition tracker for regular updates of work progress.

Three phases in each work zone

Crews will not be working on the whole length of the viaduct at the same time. The work will be concentrated in smaller sections that move up and down the waterfront in a staggered sequence of three phases:

In the example above, the work will move left (north), with Step 1 moving ahead to fence off the next frame while the demolition shifts north into the old Step 1 area. This sequence allows for an efficient movement along the structure, while reducing the length of the work zone in any given area (thus reducing the number of cross-streets closed at a given location).

How it will be removed

The viaduct will be removed one frame at a time. In most places, crews will use specialized equipment to remove the viaduct’s top and lower decks following the sequence below:

First, crews will fence off the immediate area and complete prep work and staging.

Next, crews use impact hammers to remove the roadway deck.

Next, large hydraulic munchers will remove the girders and columns that support the deck. In some places, crews will sawcut pieces of the viaduct and lift them away with cranes.

Crews will then begin removing the lower deck following the same process as described above.

Finally, crews will remove the viaduct's foundations, in some places to five feet below grade, and restore the site.

Cutting and picking method

There are several locations where specific site circumstances - like nearby buildings or railroad tracks - require Kiewit to remove the viaduct using a different method. In these places, crews will cut the viaduct into pieces with saws, then lift them off one by one with cranes.

The photo above, taken on March 4, 2019, shows two cranes lifting a girder from the Columbia Street on-ramp. Crews hammered out the road deck, then lifted the girders off one by one. The girders were placed on the ground below and broken apart. This method of work is slower but necessary in certain circumstances.

WSDOT and Kiewit's goals are to complete the work safely and quickly while reducing where possible the work's disruption to people and property nearby.

Protecting buildings, infrastructure and utilities

Kiewit will enclose active construction areas with fencing.

When working in close proximity to buildings, Kiewit will use temporary barriers and heavy nets to keep debris contained. Debris containment materials will not be attached to buildings.

Trees will be protected with ecology blocks and protective wrapping.

Temporary building and parking access restrictions will be in effect according to previously negotiated Temporary Construction Easements.

If lighting is needed during work hours, it will face the project site and be shielded to minimize its impact on nearby residents and businesses. Lights will be used only during active operations.

Vibration will be monitored, and cushioning placed beneath the viaduct to soften the impact from falling rubble. For safety and vibration reasons, demoed pieces of the viaduct will generally be less than 10" in diameter.

Noise

The sound environment along the waterfront has changed with the viaduct’s closure. Construction noise will be more pronounced now that traffic is not on the viaduct. The loudest work will be when the contractor uses impact hammers to remove the viaduct road decks. This work will take one to several days per section of roadway deck. The tall muncher equipment used to crush the viaduct’s bents and columns will not be as loud.

The noisiest demolition work will occur only during the daytime. The allowable hours of impact work are:

7 a.m. to 8 p.m. weekdays

9 a.m. to 8 p.m. Saturdays

9 a.m. to 5 p.m. Sundays and holidays

Other work activities are permitted at night, but they must remain within more strict noise limits. Electronic systems will collect data from noise monitors and will automatically alert superintendents when crews approach or exceed noise limits. An inspector will also be onsite during any night work to investigate hotline calls about noise, and to ensure that any night work stays under permitted noise limits.

The contractor will use other best practices to limit nighttime noise, such as not slamming truck tailgates, and not using compression brakes or pure-tone backup alarms.

Dust and water

Kiewit will control dust by spraying mist down onto the concrete as it is broken up. Manual observers and spray crews will also be available if needed. The work is designed to avoid creating plumes of dust, so walking near the work zone will not pose any inhalation health hazards.

The contractor captures all water that lands on the job site. That water is reused for more dust control as much as possible. Eventually, the water is treated in a baker tank system and then discharged into the sewer system under a King County sewer permit. This ensures no polluted water runs into Elliott Bay.

Hazardous materials

The viaduct was tested prior to the start of construction, and all potential hazardous materials were safely removed from the structure prior to the start of demolition.

Any soil believed to be hazardous will be tested, analyzed and disposed of at an off‑site hazmat facility. No asbestos was found in the viaduct, but any materials suspected of containing it will be tested as required.